AD590
Table 4. Thermal Resistance
θ
JC + θCA
(°C/Watt)
τ (sec)1
F
T
FINAL
Medium
H
F
H
Aluminum Block
Stirred Oil2
Moving Air3
30
42
10
60
0.6
1.4
0.1
0.6
With Heat Sink
Without Heat Sink
Still Air
45
115
–
190
5.0
13.5
–
10.0
–t/τ
)
T(t) = T
+ (T
– T ) × (1 – e
INITIAL
INITIAL
FINAL
With Heat Sink
Without Heat Sink
191
480
–
650
108
60
–
30
1 τ is dependent upon velocity of oil; average of several velocities listed above.
2 Air velocity @ 9 ft/sec.
T
INITIAL
τ
4τ
TIME
3 The time constant is defined as the time required to reach 63.2% of an
instantaneous temperature change.
Figure 15. Time Response Curve
The time response of the AD590 to a step change in
temperature is determined by the thermal resistances and the
thermal capacities of the chip, CCH, and the case, CC. CCH is
about 0.04 Ws/°C for the AD590. CC varies with the measured
medium, because it includes anything that is in direct thermal
contact with the case. The single time constant exponential
curve of Figure 15 is usually sufficient to describe the time
response, T (t). Table 4 shows the effective time constant, τ, for
several media.
Rev. D | Page 9 of 16
ADI [ ADI ]
